Question

1) Action potential

a) Explain how an action potential moves down a cell wall. Be very specific about what generates a force, and what exactly moves. Explain how the membrane chemistry play a role.

b) Explain what electrical signals are available for measuring in the case of the heart, brain and nervous system, and muscles. Give details regarding timing and magnitude.

c) Explain how the signals described in b) are measured in practice. Give details about techniques or particular circuits which allow the measurement of very small signals. Include any necessary diagrams.

Answer 1

a.An action potential is part of the process that occurs during the firing of a neuron. During the action potential, part of the neural membrane opens to allow positively charged ions inside the cell wall and negatively charged ions out. This process causes a rapid increase in the positive charge of the nerve fiber.

This starts with a channel opening for Na⁺ in the membrane. Because the concentration of Na⁺ is higher outside the cell than inside the cell wall by a factor of 10, ions will rush into the cell that are driven largely by the concentration gradient. Because sodium is a positively charged ion, it will change the relative voltage immediately inside the cell relative to immediately outside. The resting potential is the state of the membrane at a voltage of -70 mV, so the sodium cation entering the cell will cause it to become less negative. This is known as depolarization, meaning the membrane potential moves toward zero.As the membrane potential reaches +30 mV, other voltage-gated channels are opening in the membrane. These channels are specific for the potassium ion. A concentration gradient acts on K⁺, as well. As K⁺ starts to leave the cell, taking a positive charge with it, the membrane potential begins to move back toward its resting voltage. This is called repolarization, meaning that the membrane voltage moves back toward the -70 mV value of the resting membrane potential.

b.electrical signals are available for measuring in the case of the heart are in the form of ECG(electrocardiogram)

Brain:functional Magnetic Resonance Imaging (fMRI), magnetoencephalography (MEG) and electroencephalography (EEG)

Nervous system: electrophysiology

Muscles:EMG Electromyography

c.Details :

Heart: Electrocardiography measures the electrical activity of the heart by using electrodes placed on the skin. For the heart to contract and pump blood, a series of coordinated electrical signals are sent to the heart by the autonomic nervous system.The heart is a two stage electrical pump and the heart's electrical activity can be measured by electrodes placed on the skin. The electrocardiogram can measure the rate and rhythm of the heartbeat, as well as provide indirect evidence of blood flow to the heart muscle.

Brain:When using EEG, you are measuring electrical activity generated by the various cortical layers of the human brain. Specifically, electrical signals are picked up from gray matter regions, which have high densities of pyramidal cells that communicate with each other. It is typically noninvasive, with the electrodes placed along the scalp, although invasive electrodes are sometimes used, as in electrocorticography.

Nervous system:Using a series of probes, known as electrodes, we can detect small changes in membrane voltage and the sensitivity of the technique can vary, so that we can detect the activity of a single ion channel in one neuron, to the activity of large ensembles of neurons.Allows us to detect the activity of large ensembles of neurons using electrodes placed on the scalp. These tiny probes are known as microelectrodes and can be made either from very thin metal, or from class capillaries which have been heated and stretched to a tiny point and then filled with a salty solution that mimics the intracellular contents of the cell.

Muscles:Electromyography (EMG) measures muscle response or electrical activity in response to a nerve's stimulation of the muscle. The test is used to help detect neuromuscular abnormalities. During the test, one or more small needles (also called electrodes) are inserted through the skin into the muscle.EMG signals are recorded by placing electrodes close to the muscle groups. When the muscle is activated, the length of the muscle decreases and the muscle, skin and electrodes move with respect to one another. At that time, the electrodes will show some movement artifacts